Definitely not dandelions. Dandelions have a broad toothy leaf. These leaves are narrow and spiky. Additionally their seed heads are twice as full and are rarely over 12" tall.
If it has slightly purple flowers, then I am going with Thistle. They can be so very invasive. I wasn't smart enough to get rid of the first one, because I liked the blossoms. It took me forever to eradicate it, and am glad that I did.
This is a flower, wildflower can't remember but i to believe that it is a goat's beard. comes in alot of wild flower mixes, will stick for awhile so if you don't want them, diggin up before seed blows away.
My children's greatgrandmother used to have me pick one and spray it with Hairspray to preserve it as they are beautiful... Yup, it's a weed, but rare nowadays...
Goatsbeard. It's evident by the foliage in the photo. They are very pretty if you pick it carefully and spray it with hairspray or clear coat spray. Makes a nice detail in an arrangement.
Thanks everyone. I found pics of goatsbeard that are exactly like this. I think every flower is a 'weed'. It's just that people decided which ones they did or didn't like. I like these. So, I call them a flower! LOL.
Allium?
http://www.youtube.com/watch?v=UQ_QqtXoyQw